All smoke detectors are powered by utility power with a 9-volt dry cell battery as a backup in time of power failure. Currently, there is no convenient or effective method to visually determine the status of the battery used in a smoke detector. In addition, it is very hard to manually check the power level of the battery because smoke detectors are usually mounted to the ceiling. Therefore, an objective of the present invention is to provide an apparatus which visually displays the amount of “power” remaining in the battery of the smoke detector.